Pacific tree frog has severely swollen mouth/ lips

[killerecho]

It's hard to say what could be the cause without a picture of the swollen area. I doubt it's due to mating. Opening mouth and arching head back might just be shedding behavior.

When is the last time you've seen it eat? Ever try feeding with tongs? What does the habitat look like? Is there any possibility of impaction? More information may help, but if it does turn out to be an infection or disease of some kind, your best and only option is to take it to a vet.